JP2007232556A - Optical displacement sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical displacement sensor capable of precisely detecting the peak position of light receiving level distribution of reflected light from a measured object even when the measured object is not a diffusing/reflecting surface. <P>SOLUTION: This optical displacement sensor comprises a projecting element 1 for radiating light to the measured object M, and an image sensor 4 for receiving reflected light of the radiated light from the measured object M, and measures the distance to the measured object M based on the peak position of the light receiving level distribution of the image sensor 4. This optical displacement sensor comprises a peak position determining means 8 for determining the peak position based on a threshold Th of the light receiving level, and a threshold setting means 7 for adjusting and setting the threshold Th, based on the magnitude of the amount of received light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention detects the displacement of the measurement object by measuring the distance to the measurement object based on the light reception data from the image sensor that receives the reflected light from the measurement object irradiated with light by the light projecting element. The present invention relates to an optical displacement sensor.

Conventionally, in order to measure the movement of an object, the size of the object, etc., an optical displacement sensor that detects the displacement of the measurement object by measuring the distance to the measurement object by a triangulation method (for example, , See Patent Document 1). As shown in FIG. 5, this optical displacement sensor irradiates the measurement object M with the light emitted from the light projecting element 1 through the light projection lens 2, and reflects the reflected light from the measurement object M through the light receiving lens 3. Light is received by the image sensor 4 and the distance to the measuring object M is measured based on the light receiving spot position of the reflected light to the image sensor 4. Therefore, for example, when the measurement object M is displaced from the illustrated position of the solid line to the illustrated position of the two-dot chain line, the light receiving spot position of the reflected light from the measurement object M on the image sensor 4 is indicated by an arrow. Therefore, the displacement amount of the measuring object M can be detected based on the change in the light receiving spot position of the reflected light.
JP-A-62-218802

  The detection of the light receiving spot position of the reflected light to the image sensor 4 is performed as follows, for example. FIG. 6A shows an example of the waveform of the received light level distribution of the reflected light incident on the image sensor 4, and two intersections between the preset threshold value Th of the received light level and the waveform of the received light level distribution. After obtaining the pixel coordinates L1 and L2 on the image sensor 4, the intermediate value between the two pixel coordinates L1 and L2 is obtained by calculation [(L1 + L2) / 2]. The pixel coordinates P calculated by this calculation are used as the light receiving spot position of the reflected light to the image sensor 4 for the subsequent calculation of the distance to the measurement object M. If the light irradiation surface of the measurement object M is a smooth diffuse reflection surface, the reflected light is uniformly reflected in all directions, that is, diffusely reflected. As shown in FIG. 6A, the waveform is symmetrical with respect to the peak position of the light reception level, and the pixel coordinates P calculated as described above are the light reception spot positions of the light reception level TP at the peak position of the light reception level distribution. Match.

  However, for example, when there are fine irregularities on the light irradiation surface of the measuring object M, or when the measuring object M is translucent, uneven light reflection or part of incident light is transmitted. As shown in FIG. 6B, the light reception level distribution in the image sensor 4 may not have a symmetrical waveform with respect to the peak position P indicating the light reception peak level TP. In this case, the light receiving spot position P1 [= (L1 + L2) / 2] of the reflected light obtained by the calculating means described above has an error E with respect to the actual peak position P, and this light receiving spot position P1 is reflected by the reflected light. When used as a light receiving spot position, the distance to the measurement object M cannot be measured accurately.

  The present invention has been made in view of the above-described conventional problems. Even when the measurement object is not a diffuse reflection surface, the peak position of the light reception level distribution of the reflected light from the measurement object can be easily and accurately determined. An object of the present invention is to provide an optical displacement sensor that can be detected.

  In order to achieve the object, an optical displacement sensor according to the present invention includes a light projecting element that irradiates light to a measurement object, an image sensor that receives reflected light from the measurement object of the irradiated light, and A peak position determination means for measuring a distance to the measurement object based on a peak position of a light reception level distribution of the image sensor, and determining the peak position based on a threshold value of the light reception level And threshold setting means for adjusting and setting the threshold based on the amount of light received by the image sensor.

  According to this configuration, when the threshold setting unit adjusts and sets the threshold of the received light level based on the magnitude of the received light amount of the image sensor, for example, based on the total received light amount of each pixel of the image sensor, Based on the set threshold value, the peak position determination means determines the peak position of the light reception level distribution of the image sensor. For example, the peak position determination means determines an intermediate position between two coordinates equal to the threshold value in the light reception level distribution as the peak position, as in the conventional case. Thus, as described below, even when the light reception level distribution received by the image sensor with the light irradiation surface of the measurement object not being a diffuse reflection surface is a waveform that is asymmetrical with respect to the peak position, the determined peak position However, it approaches the actual light receiving peak position of the light receiving level distribution.

  That is, when the light irradiation surface of the measurement object is not a diffuse reflection surface, the received light level distribution of the image sensor is a distorted waveform that is asymmetrical with respect to the peak position when viewed as a whole. From the viewpoint of the characteristic, when only the distribution portion on the head side having a relatively high specific light receiving level or higher is extracted and viewed, the waveform is almost symmetrical with respect to the peak position. In addition, the waveform distorted in this way generally has a large area (amount of received light) due to the wide base of the waveform. Therefore, the light reception level of the threshold value adjusted and set individually corresponding to the magnitude of the light reception amount becomes high corresponding to the specific light reception level. As a result, if the peak position in only the distribution part on the head side that is equal to or greater than the threshold in the light reception level distribution of the image sensor is determined, the peak position is close to the actual peak position of the light reception level distribution. The distance to the measurement object can be accurately measured. Further, even when the distribution on the head side is not sufficiently symmetrical, since the two pixel coordinates that match the threshold approach due to the increase in the threshold value, the peak position is between the two pixel coordinates with a narrow peak position. Thus, the peak position can be obtained more accurately.

  In the present invention, the threshold value setting means sets the threshold value based on an average value of the light reception level distribution. According to this configuration, the intensity of the reflected light is different corresponding to the difference in reflectivity depending on the material and surface state of the measurement symmetrical object, and the amount of light received by the image sensor is increased or decreased accordingly. The light reception level of the threshold calculated based on the average value is a relatively high light reception level that is close to the peak position of the light reception level for each light reception level distribution with different waveforms corresponding to the magnitude of the light reception amount. As a result, the actual peak position can be determined with high accuracy from the light reception level distribution near the left-right symmetry higher than the threshold value.

  In the present invention, as the image sensor, for example, a linear image sensor using a CMOS transistor or a charge coupled device can be used.

  Furthermore, in the present invention, there is provided peak position correcting means for manually correcting the peak position. As a result, after adjusting and setting the threshold of the light reception level, even if it is the peak position of the light reception level distribution determined based on this threshold, depending on the material and surface condition of the measurement object, In such a case, for example, while viewing the display screen of the received light level distribution, the peak position on the screen is forcibly shifted by manually operating the peak position correction means, It can be modified to match the actual peak position of the level distribution.

  According to the optical displacement sensor of the present invention, the threshold setting means for adjusting and setting the threshold of the received light level based on the magnitude of the received light amount of the image sensor, and the received light level distribution of the image sensor based on the set threshold. And a peak position determination means for determining the peak position, so that the received light level distribution at the image sensor has a waveform that is asymmetrical with respect to the peak position in response to the measurement object not being a diffuse reflection surface. Even if it exists, the light reception peak position in the light reception level distribution of an image sensor can be determined easily and correctly.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an optical displacement sensor according to an embodiment of the present invention. A main body portion A of this optical displacement sensor irradiates light to a measurement object M through a light projection lens 2. 1 and a linear image sensor 4 that receives reflected light from the measurement object M of the irradiated light through the light receiving lens 3, and the threshold of the light reception level is adjusted based on the amount of light received by the image sensor 4. Threshold setting means 7 for setting, peak position determining means 8 for determining the pixel coordinates of the peak position of the received light level distribution in the image sensor 4 based on the threshold of the received light level set by the threshold setting means 7, and this peak position determination Based on the pixel coordinates of the peak position determined by the means 8, a distance to a certain reference surface measurement object M, for example, from the front surface of the main body A facing the measurement object M to the measurement object M. It includes a distance calculating means 9 for outputting a distance signal RS by measuring the distance D, and a light projecting device drive circuit 10 for driving the light projecting device 1.

  Further, the optical displacement sensor includes, as an external device, screen display means (monitor) 11 that displays the peak position determined by the peak position determination means 8 together with the received light level distribution received by the image sensor 4, and the screen display means. When the peak position determined by the peak position determination means 8 displayed in 11 has an error with respect to the actual peak position of the received light level distribution being displayed at the same time, the manual operation means 12 for correcting the error manually. And has. The main body A has a peak position correcting means 13 by correcting the peak position determined by the peak position determining means 8 based on the correction command signal input from the manual operation means 12.

  For example, a laser diode is used for the light projecting element 1, and this laser diode is controlled by the light projecting element driving circuit 10 so as to emit light at a predetermined light projecting power and time. As the linear image sensor 4, a CMOS type transistor or a charge-coupled device (CCD) linearly arranged is used. In this charge coupled device (CCD), each arranged pixel individually accumulates signal charges proportional to the intensity of incident light, and sequentially transfers each signal charge accumulated in each pixel. Thus, the received light level distribution can be obtained based on the amount of reflected light received by the arranged pixels.

  As shown in FIG. 2, the threshold setting means 7 obtains the received light level (the intensity of the received light signal) for each of the pixels A to L of the image sensor 4 and adds the obtained received light levels. After calculating the sum of the received light amounts of the image sensor 4, the sum of the received light amounts is divided by the number of pixels received by the image sensor 4, and an average value of the received light amount of each pixel received is calculated. Then, a threshold value Th is calculated by multiplying a constant set in advance corresponding to the reflectance of the measurement object M to be measured, and this threshold value Th is set and inputted to the peak position determination means 8.

Therefore, as is clear from the comparison between FIG. 3A and FIG. 3B, the threshold value set by the threshold value setting means 7 corresponding to the received light level distribution having different waveforms each time the image sensor 4 receives light. Th1 and Th2 are high levels that are lower than the peak levels TP1 and TP2 in each received light level distribution and relatively close to the peak levels TP1 and TP2. For this reason, the head side higher than the threshold values Th1 and Th2 in the light reception level distribution is substantially symmetrical with respect to the peak position P. Even if the distribution on the head side is not sufficiently symmetrical, the peak position is narrow because the two pixel coordinates L1 and L2 that match the threshold values Th1 and Th2 approach each other because the threshold value increases. Driven between the two pixel coordinates L1 and L2. As a result, the peak position determined by the above-mentioned [(L1 + L2) / 2], that is, the intermediate value of the light receiving positions matching the threshold values Th1 and Th2, based on the light receiving levels of the set threshold values Th1 and Th2, is the actual light receiving level distribution. Is substantially coincident with the peak position P. That is, the accuracy of peak position determination is improved by using the average value. Further, the peak position P can be easily obtained by simply calculating the average value and the intermediate value.

  Therefore, the peak position determination unit 8 updates and registers the threshold values Th1 and Th2 input from the threshold setting unit 7 in place of the currently set threshold values, and then the two positions of the threshold values Th1 and Th2 and the waveform of the received light level distribution. After obtaining the pixel coordinates L1 and L2 on the image sensor 4 at the intersection, the pixel coordinate P at the midpoint position between the two pixel coordinates L1 and L2 is calculated [(L1 + L2) / 2]. The peak position of the received light level distribution is determined. As a result, even when the light receiving surface distribution of the measuring object M is not a diffuse reflection surface and the received light level distribution at the image sensor 4 is asymmetrical with respect to the peak position, the peak position determining means 8 The determined pixel coordinates P of the peak position are well matched with the actual peak position because the peak position is determined from the head-side distribution close to the peak in the received light level distribution.

  Here, since the threshold setting means 7 adjusts and sets the thresholds Th1 and Th2 based on the average value of the received light level distribution, the accuracy of peak position determination is improved as described above. For the purpose of extracting the distribution portion of the head that is symmetrical with respect to the peak position in the light reception level distribution, when the light reception level of eyes higher than the conventional one is fixedly set as a threshold value, the light irradiation of the measuring object M is performed. When the light reflectance is low, such as black, when the peak position of the received light level distribution falls below the threshold, or when the light irradiation surface of the measuring object M is white, the light reflectance is high. In addition, there is a problem that an asymmetrical waveform portion is included in the distribution of the light reception level distribution equal to or higher than the threshold light reception level (see FIG. 6B).

  As described above, the threshold values Th1 and Th2 are set based on the magnitude of the amount of received light, and the material of the measurement object M and the peak position are set so as to be accurately determined based on the threshold values Th1 and Th2. Depending on the surface state, a slight shift may occur with respect to the actual peak position. Therefore, the occurrence of such a problem is suppressed as follows. On the screen display means 11, as shown in FIG. 4, the peak position P0 of the light reception level distribution determined by the peak position determination means 8 is displayed together with the waveform of the light reception level distribution and the threshold Th, and the peak position being displayed. When P0 is deviated from the actual peak position P of the received light level distribution, it can be visually recognized at a glance. In that case, an operation for eliminating the error is performed by the manual operation means 12 of FIG. As a result, the peak position correcting means 13 outputs a position shift signal corresponding to the setting input from the manual operating means 12 to the peak position determining means 8 and is displayed on the screen display means 11 as shown in FIG. Since P0 is forcibly shifted in the left-right direction, the determination peak position P0 is shifted until it matches the actual peak position P of the received light level distribution while viewing this display screen. After that, the peak position determination means 8 stores the shift amount of the peak position by the manual operation, and corrects the peak position calculated by itself by the shift amount to determine an accurate peak position.

  When the determination based on the threshold value that matches the average value of the received light level distribution causes an error in the peak position, the error is reduced by appropriately setting the average value multiplied by a constant larger than 1 or a constant smaller than 1 as the threshold value. Can be suppressed.

It is a block diagram which shows the optical displacement sensor which concerns on one Embodiment of this invention. It is a characteristic view which shows the setting method of the threshold value by the threshold value setting means in the optical displacement sensor same as the above. (A), (b) is a characteristic view which shows the relationship between the light reception level distribution in a different measuring object, and the threshold value set corresponding to this. It is a figure which shows the display screen of a light reception level. It is the schematic for demonstrating the distance measurement by an optical displacement sensor same as the above. (A), (b) is a characteristic view which shows the relationship between the light reception level distribution and threshold value in the different measuring object in the conventional optical displacement sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light projection element 4 Image sensor 7 Threshold setting means 8 Peak position determination means 13 Peak position correction means (correction means)
M Measurement object Th, Th1, Th2 Threshold

Claims (3)

A light projecting element that irradiates light to the measurement object; and an image sensor that receives reflected light from the measurement object of the irradiated light, and based on a peak position of a light reception level distribution of the image sensor. An optical displacement sensor that measures the distance to a measurement object,
Peak position determination means for determining the peak position based on a threshold of the light reception level;
Threshold setting means for adjusting and setting the threshold based on the amount of light received by the image sensor;
Optical displacement sensor with   2. The optical displacement sensor according to claim 1, wherein the threshold setting means sets the threshold based on an average value of the light reception level distribution. 3. The optical displacement sensor according to claim 1, further comprising correction means for manually correcting the peak position.

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